Add a offline mode support from a service worker.
The service worker will cache the assets and the
visited pages to be able to work offline.
Created a fallback page for when the user is offline
and tries to access a page that is not cached.
When we use the static mode, Next.js want that we
build our resource pages at build time. But we can't
do that because users can create a resource at runtime.
So we redirect thanks to ngnix when we see that
a resource page is not found.